Europium complex nanoclusters were encapsulated inside silica colloidal spheres by a wet-chemical method. The hybrid spheres were characterized to possess a core-shell structure by transmission electron microscopy. The spheres present strong characteristic emissions of Eu3+ ions, and the fluorescence decay time decreases when the spheres are dispersed in two dielectric polymers. Temperature-dependent decay dynamics indicates that europium complex in sphere-polymer systems display higher spontaneous emission rate compared with free hybrid spheres in air. Our results are suggestive for optimizing the luminescence quantum yield of lanthanide complexes, and also provide a promising probe to investigate modified spontaneous emission in photonic crystals. (C) 2005 Elsevier B.V. All rights reserved.